(1) Field
The present invention relates to a method for managing the temperature implemented in a speed controller. The invention also relates to a system for managing the temperature in a speed controller.
(2) Description of the Related Art
A speed controller comprises several semiconductor power modules controlled in order to supply a pulsed voltage to an electrical load. Each semiconductor power module is, for example, composed of a case containing two IGBT transistors (Isolated Gate Bipolar Transistor), each connected to a freewheeling diode (FWD). A semiconductor component of the IGBT transistor type is characterized in particular by its junction temperature and its junction-case temperature. A heat sink is mounted on the modules so as to dissipate the heat given off by the modules when operating.
The IGBT transistors used in the semiconductor power modules are the most important and the most expensive components used in a speed controller. It is therefore necessary to protect them. To do this, their absolute junction temperature must not exceed a limiting value specified by the manufacturer and their junction-case temperature must also be kept below a limiting value. For example, if the semiconductor component is made of silicon, the limiting value of the absolute junction temperature is 150° C. and the limiting value of the junction-case temperature is 65° C. If one of the limiting values is exceeded, the semiconductor component deteriorates, which might lead to important dysfunctioning in the speed controller.
As the semiconductor power modules are integrated in increasingly compact controllers, their thermal dissipation becomes increasingly difficult and the margin between the normal operating temperatures of the semiconductor components and the limiting values is increasingly restricted. Consequently, it is necessary to implement in the controller a method for managing the temperature of semiconductor components.
To do this, several possibilities exist, depending on whether the controller comprises one or several temperature sensors. In fact, when the power semiconductors are divided into three distinct modules, each comprising two IGBT transistors and two freewheeling diodes, the temperature management is not the same as when one temperature sensor per module or a single sensor for all the modules is used. In the first case, if the temperature sensor is mounted directly under the module case, the temperature measured is that of the module case and can be dealt with directly. Conversely, in the second case, if there is a single temperature sensor located, for example, on the heat sink a certain distance from the modules, the temperature which will be measured there will not agree with the case temperature of the modules. In this latter case, with a view to carrying out the appropriate management, it is often necessary to proceed to estimations in order to know the temperature of the semiconductor components.
Methods of managing the temperature of the semiconductor modules of a speed controller have already been proposed in the prior art.
Document EP 0792008 describes a method and a device for protecting the semiconductor power modules of a controller. The method consists in calculating the thermal losses of the semiconductor components and the increase in junction-case temperature. If the increase in temperature is greater than a predetermined limiting value, the operating cycle of the semiconductor modules is adjusted so as to reduce the output current of the controller.
Document JP 2005143232 also describes a method for managing the temperature of semiconductor power modules in a speed controller. This method consists in controlling the flow of current through the controller as a function of the junction temperature of the semiconductor components.
Document U.S. Pat. No. 5,923,135 describes a control device for an electric motor comprising a control circuit equipped with several semiconductor modules. This device furthermore comprises means for estimating the junction temperature of the components of each module based on a measured temperature, means for comparing the junction temperature obtained with a limiting value and means for adjusting the output of the control circuit with a view to regulating the junction temperature at a value lower than or equal to the permitted limiting value. In particular, this document proposes a thermal model for each module. This thermal model does not, however, take account of the environment of each module and in particular of the influence of the other modules on the temperature of the module attended to.